1. Field of the Invention
The present invention relates to a single-layered electrophotographic photoreceptor, and more particularly, to an electrophotographic photoreceptor having high sensitivity and a low residual potential, thus exerting good electrostatic properties.
2. Description of the Related Art
In general, an electrophotographic photoreceptor includes a photosensitive layer including a charge generating material, a charge transporting material and a binder resin, formed on a conductive substrate. As photosensitive layers, function-separation type photoreceptors having a laminated structure in which a charge generating layer and a charge transporting layer are laminated have been widely used.
In recent years, since single layered photoreceptors may be manufactured by a simplified process are advantageous due to effective chargeability, such photoreceptors are used in positive corona discharge, and generate a small amount of ozone. Hence, the single layered photoreceptors have attracted considerable attention, and extensive studies are underway.
Representative examples of conventional single layered electrophotographic photoreceptors include a photoreceptor comprising a PVK/TNF charge transfer complex as disclosed in U.S. Pat. No. 3,484,237, a photoreceptor comprising photoconductive phthalocyanine dispersed in a resin as disclosed in U.S. Pat. No. 3,397,086, a photoreceptor comprising a thiapyrylium and polycarbonate aggregate and a charge transporting material dispersed in a resin as disclosed in U.S. Pat. No. 3,615,440. However, those photoreceptors disclosed therein are not sufficiently effective in view of electrostatic properties and are considerably limited in selection of materials. Also, since such materials are harmful, the materials are not employed any longer.
Currently, single layered photoreceptors having a charge generating material, a hole transporting material and an electron transporting material dispersed in a resin, as described in Japanese Patent Publication 54-1633, have become the subject of development. Since such photoreceptors are functionally separated for charge generation and charge transporting, a wide variety of materials may be selected. Also, since the concentration of the charge generating material may be reduced, functional and chemical durability of the photosensitive layer may be enhanced.
Single layered photoreceptors that have been proposed to date exhibit substantially the same sensitivity level as laminated photoreceptors. However, the conventional single layered photoreceptors have slow light decay characteristics at a low electrical field area, resulting in an increase of residual potential. The increased residual potential may cause reduction of an image density, causes a memory effect, and restricts a design margin of an electrophotographic device, so that a remedy is needed. The slow light decay at the low potential area may have several causes. That is, since charge generating materials uniformly distributed in the photosensitive layer form trap sites, light decay may be caused by the combination of rapid discharge due to charges transported to solid solution of a charge transporting material and a resin as main components of the photosensitive layer and slow discharge due to charge trapping and detrapping at trap sites present in a low concentration.
To attain a single layered electrophotographic photoreceptor having a small residual potential, inventors of the present invention studied compositions of electrophotographic photoreceptors, and found out that the residual potential may be effectively reduced by including a peculiar charge transfer complex (CT-complex) having a hole transporting material and an electron transporting material in a photosensitive layer, thus completing the present invention.